In practice, a servo-controlled gearbox is a conventional mechanical gearbox operated by means of servo-controllers, comprising an actuator for disengaging and engaging the friction clutch between the driveshaft and the primary input shaft of the gearbox, an actuator for selecting the transmission ratios and an actuator for engaging the selected transmission ratio.
Servo-controlled gearboxes are well known in the prior art and are used to reproduce and optimize the driver's gear change commands.
The control strategies of a control system for a servo-controlled gearbox must adapt themselves to the operating conditions of the vehicle and must maintain the driving sensation requested by the driver by means of the commands imparted to the accelerator pedal.
A control system for a servo-controlled gearbox is known from U.S. Pat. No. 6,389,346 held by the present applicant. The system comprises an electronic control unit connected to a plurality of sensors for detecting the operating conditions of the vehicle, including a potentiometric sensor for detecting the position of the accelerator pedal, to the actuators of the gearbox, and to the actuators controlling the power delivered by the vehicle's propulsion system, in order to permit the integrated control of the propulsion system and the gearbox during a gear change operation.
The detection of the position of the accelerator pedal enables the driver's intentions to be correctly recognized.
The operation of the control unit is based on a reference model in which the actuator command signals are determined by means of a mathematical model of the driving behaviour, which is designed to adapt the behaviour of the vehicle in terms of comfort and performance, in the various stages of the gear change, according to the commands imparted by the driver by means of the accelerator pedal and a command lever or push button for selecting the transmission ratio, in other words for requesting a change to a higher or lower ratio.
In both a gear-change operation and a driving-away manoeuvre, the vehicle's propulsion system changes its mode of operation from clutch partially disengaged to clutch engaged. At the instant the clutch bites, the inertia applied to the engine changes virtually instantaneously, causing discontinuities in the vehicle's acceleration, specifically a negative change of acceleration which may be perceived by the driver and reduces the performance of the system.